Optical disk having areas of different recording densities or functions

ABSTRACT

An optical disk includes a standard area of a standard recording density provided on an inner peripheral side and a high density area of a higher recording density provided on an outer peripheral side. In each of the standard area and the high density area, a program area is provided so that an independent program can be recorded in each program area. In, one aspect of the invention, an optical disk includes, from the inner periphery to the outer periphery of the disk, a ROM area for read-only purpsoe, a RAM area in which information can be rewritten and a WO area in which information can be written only once.

BACKGROUND OF THE INVENTION

This invention relates to optical disks such, for example, as a CD, aCD-ROM, a CD-R, a CD-RW, a CD-I, a MD and a DVD and, more particularly,to optical disks having two areas of different recording densities. Thisinvention relates also to optical disks having areas of differentfunctions and to a method of manufacturing such optical disks and alsoto a method of recording information on such optical disks.

Optical disks such as a CD, a CD-ROM and a CD-R having a standardrecording density have a track pitch of 1.6 μm and a linear velocity of1.2 m/s to 1.4 m/s. With the recent tendency to using a laser beam spotof a smaller diameter, optical disks having a higher recording densityhave been developed. For example, a DVD-ROM has a track pitch of 0.74 μmand linear velocity of 3.94 m/s and has a recording capacity which isseven times as large as a CD.

In case a large amount of data such as a moving picture data is to berecorded in coping with the tendency to increasing the recordingcapacity of an optical disk, an optical disk having a high recordingdensity may be used.

An optical disk drive device which can cope with media having a highrecording density can drive also an optical disk having a lowerrecording density whereas an optical disk drive device which canreproduce only a CD having a standard recording density cannot drive anoptical disk having a high recording density. For this reason, when anoptical disk having a high recording density is used, conventional CDdrive devices cannot reproduce such optical disk so that drive deviceswhich can reproduce it are limited.

It is, therefore, a first object of the present invention to provide anoptical disk which has a much larger recording capacity than aconventional optical disk of a standard recording density and yet isapplicable also to a drive device which can reproduce only theconventional optical disk of the standard recording density.

Known also in the art of optical disks is one having areas of differentfunctions. For example, Japanese Patent Application Laid-open 9-7223discloses an optical disk having a ROM area used for read-only purposeand a RAM area which can be rewritten. This optical disk has advantagesof both a read-only disk and a rewritable disk in that a large amount ofcopies can be produced from a software by using the ROM area while datacan be written in the RAM area.

In this type of optical disk, information recorded in the ROM areacannot be erroneously overwritten but information recorded in the RAMarea can be erroneously overwritten. In a floppy disk, overwriting canbe inhibited but this can be made only for the entire disk and not foronly a part of data which is important.

It is, therefore, a second object of the invention to provide an opticaldisk in which a recording mode can be selected depending upon the degreeof importance of information.

It is a third object of the invention to provide a method for recordinginformation on this optical disk.

It is a fourth object of the invention to provide a method formanufacturing this optical disk.

SUMMARY OF THE INVENTION

For achieving the first object of the invention, there is provided anoptical disk comprising a first area of a standard recording, densityformed on an inner peripheral side of the optical disk, a second area ofa higher recording density than the first area formed on an outerperipheral side of the optical dish, and a program recording areaprovided in each of the first and second areas, said program recordingarea being capable of recording a program independently of each otherprogram recording area.

According to the invention, by using a different mode of recording foreach of the first and second areas such as recording a standard programin the first area and a higher degree of program in the second area, asubstantial degree of program can be reproduced with a conventionalstandard optical disk drive so that the optical disk according to theinvention can provide interchangeability between the conventionaloptical disk drive and an optical disk drive exclusively used for anoptical disk of a high recording density. Moreover, by providing a highrecording density area in the outer peripheral side of the optical disk,the recording capacity can be increased substantially as compared withthe conventional CD and the data transfer rate can also be increased.

Either or both of the first and second areas may be constructed as aread-only area. Likewise, either or both of the first and second areasmay be constructed as an area which is capable of both writing andreading.

In one aspect of the invention, depth from a surface on which laser beamis irradiated to a recording surface of the second area is smaller thandepth from the surface on which laser beam is irradiated to a recordingsurface of the first area. By this arrangement, a layer of a highrefractive index may be made thinner in the high recording density areathan in the standard recording density area and, accordingly, the amountof deviation of a beam spot caused by deflection or inclination of anoptical disk can be reduced.

In another aspect of the invention, a border area between the first areaand the second area is formed as a mirror area where all laser beam isreflected. By this arrangement, the largest level of reflected beam canbe obtained in this mirror area and, accordingly, this area can bedistinguished from the other areas by a simple signal processing. Thisarrangement is particularly effective in the high speed searchoperation.

In another aspect of the invention, a border area between the first areaand the second area is an area where recording density changes graduallyfrom the standard recording density to the higher recording density. Bythis arrangement, a tracking control can be made by gradually changing aservo parameter from the first area to the second area.

In another aspect of the invention, the first and second areas have alead-in area, a program area and a lead-out area and TOC information ofthe program area of each area is recorded in the lead-in area of eacharea. By this arrangement, each area can be controlled independently anda drive device which can reproduce only an optical disk of the standardrecording density can be accessed as if the optical disk was one havingthe first area only.

In still another aspect of the invention, the first area has a lead-inarea and a program area and the second area has a program area and alead-out area, TOC information of the program area of the first andsecond areas being recorded in the lead-in area of the first area. Bythis arrangement. TOC information of all areas can be obtained byaccessing the first lead-in area only so that initial time of the drivedevice can be saved.

For achieving the second object of the invention, there is provided anoptical disk comprising a rewritable area (hereinafter refereed to as“RAM area” in which recorded information can be rewritten and a writeonce area (hereinafter referred to as “WO area” in which information canbe recorded only once.

The optical disk may further comprise a read-only area (hereinafterrefereed to as “ROM area”) capable of only reading recorded information.

According to this aspect of the invention, processing, addition andrenewal of data can be made in the RAM area and important informationfor which processing has been completed and no more change needs to bemade can be recorded in the WO area. Therefore, overwrite inhibit can beapplied only to important data while freedom of rewriting is retained,so that the scope of information recording operation can besignificantly broadened.

By further providing the ROM area, a further broadened scope of use canbe ensured such that a predetermined program may be recorded in the ROMarea and data input in accordance with this program may be processed inthe RAM area and result of the processing may be recorded in the WOarea.

For achieving the third object of the invention, there is provided amethod for recording information in the optical disk as described abovecomprising a step of recording information which has been rewritten inthe rewritable area in the write once area as overwrite inhibitinformation in accordance with a predetermined command.

For achieving the fourth object of the invention, there is provided amethod for manufacturing the optical disk as described above comprisingsteps of a first masking step of covering a portion of an optical disksubstrate other than a first area with a masking material, a step offorming an alloy layer consisting of an optomagnetic material or a phasechanging material on the substrate masked by the first masking step, afirst masking removing step of removing the masking material from thesubstrate formed with the alloy layer, a second masking step of coveringa portion of the substrate other than a second area which is differentfrom the first area with a massing material, a step of forming adyestuff layer which changes with heat on the substrate masked by thesecond masking step, a second masking removing step of removing themasking material from the substrate formed with the dyestuff layer, anda step of forming a reflecting layer on the substrate formed with thealloy layer in the first area and the dyestuff layer in the second area.

According to this aspect of the invention, the RAM area can be formed byproviding an alloy layer consisting of an optomagnetic material or aphase changing material and the WO area can be formed by providing adyestuff layer which changes with heat. Accordingly, by performingmasking in accordance with these areas to selectively form the alloylayer and the dyestuff layer, the optical disk of this aspect of theinvention can be produced.

These and other objects and features of the invention will becomeapparent from the description made below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION

In the accompanying drawings

FIG. 1 is a plan view showing recording areas of an embodiment of theoptical disk made according to the invention:

FIG. 2 is a partial sectional view of the optical disk;

FIGS. 3A to 3D are enlarged views of the respective recording areas ofthe optical disk;

FIG, 4 is a view showing an example of the optical disk in which depthof recording differs in each area;

FIGS. 5A and 5B are enlarged views showing the border areas of theoptical disk;

FIG. 6 is a block diagram showing an example of drive device for drivingthe optical disk;

FIG. 7 is a flow chart illustrating the operation of the drive device;

FIGS. 8A to 8C are diagrams showing relation between radius of recordingand absolute time in comparison with a conventional optical disk;

FIG. 9 is a diagram for explaining a method for detecting the borderarea of the optical disk;

FIG. 10 is a plan view of another embodiment of the optical disk madeaccording to the invention;

FIG. 11 is an A—A sectional view of FIG. 1:

FIGS. 12A to 12J are diagrams showing a method for manufacturing theoptical disk of this embodiment:

FIG. 13 is a flow chart showing this method for manufacturing theoptical disk;

FIG. 14 is a block diagram showing an example of drive device fordriving this optical disk; and

FIGS. 15A and 15B are flow charts for explaining examples of recordingand reproducing of this optical disk.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of the optical disk made according to theInvention.

An optical disk 1 has a standard area 11 which constitutes the firstarea formed on the inner peripheral side of the disk, a high densityarea 12 which constitutes the second area formed on the outer peripheralside of the disk and a border area 13 formed between the two areas 11and 12. The standard area 11 is an area in which, as in a standard CD orCD-ROM, a track is formed with track pitch of 16 μm and linear velocityof 1.2 m/s to 1.4 m/s. The high density area 12 is an area in which atrack is formed with track pitch of, e.g., 1.15 μm and linear velocityof 0.96 m/s.

Referring to FIG. 2 which is a partial sectional view of the opticaldisk 10, the standard area 11 provided on the inner peripheral side ofthe optical disk 10 and the high density area 12 provided on the outerperipheral side of the optical disk 10 respectively have a lead-in areaLI, a program area PG and a lead-out area LO. More specifically, thelead-in area LI of the standard area 11 starts at the radius of. e.g.,23 mm and the program area PG of the standard area 11 starts at theradius of, e.g., 25 mm. At least 6 seconds are secured for the programarea PC and at least 90 seconds are secured for the succeeding lead-outarea LO. Since a pregap of 2 seconds or over is provided at the startpoint of the program area PG, at least 4 seconds must be secured as thenet program area This length corresponds to the rated minimum programtime.

FIGS. 3A to 3D show forms of track which the standard area 11 and thehigh density area 12 can take.

FIG. 3A shows an example of a track formed in case both the standardarea 11 and the high density area 12 are read-only areas. FIG. 3B showsan example of a track formed in case the standard area is a read-onlyarea and the high density area 12 is capable of both writing andreading. FIG. 3C is an example of a track formed in case the standardarea 11 is capable of writing and reading and the high density area 12is a read-only area. FIG. 3D is an example of a track formed in caseboth the standard area 11 and the high density area 12 are capable ofwriting and reading. In the areas which are capable of writing andreading, wobble is formed for detecting a record address.

Referring to FIG. 4, depth d from a surface 14 on which laser beam isirradiated to recording surfaces of the respective areas may be set to1.2 mm in the standard area and to a value below 1.2 mm, e.g., 0.8 mm,in the high density area. Since the portion of the optical disk betweenthe surface 14 on which laser beam is irradiated to the recordingsurfaces 15 is filled with polycarbonate, the amount of deviation of abeam spot from its desired position increases with depth d because ofdeflection or inclination of the optical disk 10. The higher therecording density, the more remarkable is the adverse effect of suchdeviation of the beam spot. Accordingly, by making the depth d smallerin the high density area 12 than in the standard area 11, this adverseeffect can be mitigated.

The border area 13 between the standard area 11 and the high densityarea 12 may be formed as a mirror area as shown in FIG. 5A in which alllaser beam is reflected. Alternatively, the border area 13 may be formedas a variable pitch area as shown in FIG. 5B in which recording densitychanges gradually from a standard recording density to a higherrecording density. It is also conceivable to connect a track of astandard pitch directly with a track of a higher density pitch but thisform of tracks is hard to manufacture. In case the mirror area is used,detection of the border area 13 is easy as will be described later. Incase the variable pitch 13 is used, there is the advantage that acontinuous tracking becomes possible by gradually changing the servoparameter from the standard area 11 to the high density area 12.

FIG. 6 schematically illustrates an optical disk drive device 20 fordriving the above described optical disk. This example is a read-onlydrive device.

An optical disk 10 is driven and rotated by a spindle motor 21 at aconstant linear velocity. An Optical pickup 22 is provided as readingmeans at a position opposite to the recording surface of the opticaldisk 10. The optical pickup 22 Is driven by a feed motor 23 in theradial direction of the optical disk 10. A read out signal from theoptical disk 10 is amplified by an RF (high-frequency) amplifier 24 andis supplied to an EFM-CIRC (cross interleaved Read-Solomon code) decoder25. The decoder 25 subjects the amplified signal to EFM demodulation andCIRC decoding and supplies its output data to a buffer memory 27 to beonce stored therein under the control of a memory controller 26 andsupplies control information to a system controller 28. Data which isonce stored in the buffer memory 27 is sequentially read out under thecontrol of the memory controller 26 and supplied to an unillustratedhost system. A servo control section 29 performs focusing and trackingcontrols of the optical pickup 22 in response to the output of the RFamplifier 24 and also controls the spindle motor 21 and the feed motor23 in accordance with a command from the system controller 28.

FIG. 7 shows a routine of reproduction of an optical disk in the abovedescribed optical disk drive device 20 with respect to a case where thedrive device 20 is a home player which can reproduce only an opticaldisk of a standard recording density and also with respect to a casewhere the drive device 20 is a high-class professional type player whichcan reproduce also an optical disk of a high recording density.

In a case where the drive device 20 is an ordinary home player, thefocus servo is started in the lead-in area LI of the standard area 11(S1) and, after starting of tracking servo (S2), reproduction of a pitsignal (S3) and starting of spindle servo (S4). TOC information is readfrom a subcode frame of Q channel in the lead-in area LI of the standardarea 11 (S5) the routine enters a reproduction command standby state(S6) and, upon in-putting of a reproduction command, the program area PGin the standard area 11 is reproduced (S7). Upon detection of thelead-out area LO of the standard area 11, the reproduction operation isfinished (S7). In this case, an arrangement is made so that reproductionis made only in the standard area 11 and the high density area 12 ishidden from the TOC information.

In a case where the drive device 20 is a high class professional typeplayer which can reproduce also the high density area 12, focus servo isstarted in the lead-in area LI of the standard area 11 (S11) and, afterstarting of tracking servo (S12), reproduction of a pit signal (S13) andstarting of spindle servo (S14), TOC information is read from thesubcode frame of Q channel in the lead-in area LI of the standard area11 (S15). At this time, the player secures information indicatingexistence of the high density area 12 from a part of the TOC information(S16). In this case, an arrangement is made so that informationincluding record position of TOC information of the high density area 12can be provided. The routine enters a reproduction command standby mode(S17). Upon inputting of a command for reproduction of the standard area11, an operation which is the same as the above described reproductionof the standard area 11 is performed (S7, S8) whereas upon inputting ofa command for reproduction of the high density area 12, TOC informationis secured from the lead-in area LI of the high density area 12 (S19)and the program area PG of the high density area 12 is reproduced (S20).Upon detection of the lead-out area LO of the high density area 12, thereproduction operation is finished (S21).

FIGS. 8A to 8C are diagrams showing relation between absolute time(ATIME) of the program area PG which is specified by the subcode andradius position (R).

In the case of a conventional CD. as shown in FIG. 8A, the absolute timeof the program area PG and the lead-out area LO changes linearly from 0to the maximum value with increase of the radius position. In the caseof the present embodiment of the invention, as shown in FIG. 8B,discontinuity in the absolute time occurs in the border area. Thelead-in area LI in both the standard area and the high density area hasno absolute time.

Detection as to whether the area in qustion is the standard area 11 orthe high density area 12 is made by referring to the absolute timewritten in TOC information. For instance, if it is written in the TOCinformation that the standard area 11 starts from absolute time “00minute 00 second 00 frame” and the high density area 12 starts fromabsolute time “10 minute 00 second 00 frame”, the end of the standardarea 11 can be detected from the lead-out area LO. Further, since in theTOC information of the high density area 12, the lead-in area LI islocated at a position which is several tens tracks reverse to thestarting time of the high density area 12, the high density area 12 canbe readily located from this information. It is therefore unnecessary toaccess the border area 13.

In the case where the optical disk 10 is of a format as shown in FIG.8C, all TOC information can be secured in the lead-in area LI of thestandard area 11. In this case, processing in the border area 13 is madein the following manner.

In the case where the border area 13 is a mirror area as shown in FIG.5A, difference in refractive index in the mirror area is utilized asillustrated in FIG. 9. In the mirror area, an RF signal of a level whichis higher than in other areas is produced and, therefore, feeding of theoptical pickup 22 is continued until the RF signal of the higher levelis detected by threshold level Vth while feed distance from the end ofthe mirror area to a target position is calculated during feeding of theoptical pickup 22. When the optical pickup 22 has been fed from the endpoint of detection of the high RF signal (end of the mirror area) to thevicinity of the target position, address is read, track number to thetarget position is calculated and tracking is performed by counting thetrack number. Reproduction is started upon detecting the address of thetarget position.

In the case where the border area 13 is a variable pitch area as shownin FIG. 5B, continuous seek operation or tracking is made possible byadjusting the servo parameter from the standard area 11 to the highdensity area 12.

According to the above described embodiment of the invention, theoptical disk 10 has the standard area 11 on the inner peripheral side ofthe disk and the high density area 12 on the outer peripheral side ofthe disk so that it can be utilized in the following ways:

(1) A standard software is recorded on the inner peripheral side and ahigh class software having a higher function is recorded on the outerperipheral side.

(2) A game software for demonstration purpose is recorded on the innerperipheral side and an actual game software is recorded on the outerperipheral side.

(3) A beginner's dictionary or a dictionary for general purpose isrecorded on the inner peripheral side and a large dictionary for aprofessional use such as medical science and physics is recorded on theouter peripheral side.

(4) Data of a part of a music piece is recorded on the inner periheralside and data of the entire music piece is recorded on the outerperipheral side.

(5) Rough map data is recorded on the inner peripheral side and moredetailed map data is recorded on the outer peripheral side.

By such application of the optical disk, the entire service can beprovided to a user having a high-class professional player and a part ofthe service, though not the entire service, can be provided to a userhaving an ordinary home player whereby the optical disk has thedemonstration effect that the user can recognize a part of the service.

Referring now to FIGS. 10 to 15, another embodiment of the inventionwill be described.

FIG. 10 schematically illustrates another embodiment of the optical diskmade according to the invention.

An optical disk 31 has, from the inner periphery to the outer periphery,a ROM ( read-only memory) area 32 used for reading only, a RAM (randomaccess memory) area 33 in which recorded information can be rewrittenand a WO (write once) are 34 in which information can be written onlyonce.

In FIG. 11 which is a sectional view taken along arrows A—A in FIG. 10,the optical disk 31 has a transparent substrate 41 in which lands 42 andgrooves 43 (and pits in the ROM area 32) are formed with the intervalof, e.g., 1.6 82 m. Alloy layer 44 consisting of an optomagneticmaterial such, for example, as GdTbCuFe and GdCuFe or a phase changingmaterial such, for example, as GeSbTe and AgInSbTe is formed in the RAMarea 33 and a dyestuff layer 45 consisting of, e.g.. cyanin dyestuff.phthalocyanine dyestuff and diazo type dyestuff is formed in the WO area34. A reflectig film 46 consisting of Al is formed over these areas andalso the ROM area 32 and a protective layer 47 is formed over the entirereflecting film 46.

FIGS. 12A to 12I are sectional views illustrating a method formanufacturing this optical disk 31 and FIG. 13 is flow chart showing themanufacturing method.

(1) First, a substrate 41 in which the lands 42 and grooves 43 (alsopits in the ROM area 32) are formed is produced (FIG. 12A and S31 inFIG. 13.

(2) Then, the ROM area 32 and the WO area 34 other than the RAM area 33of the substrate 41 are masked with a masking material 48 such as a film(FIG. 13B and S32 of FIG. 13).

(3) The alloy layer 44 is formed thereon by spattering or vapordeposition (FIG. 12C and S33 of FIG. 13).

(4) The masking material 4, is removed (FIG. 12D and S34 of FIG. 13).

(5) Then, the ROM area 32 and the RAM area 33 owner than the W0 area 34of the substrate 41 are masked with a masking material 49 such as a film(FIG. 12E and S35 of FIG. 13).

(6) The dyestuff layer 45 is formed thereon by coating dyestuff by spincoating (FIG. 12F and S36 of FIG. 13).

(7) The masking material 49 is removed (FIG. 12G and S37 of FIG. 13).

(8) The reflecting film 46 is formed thereon by spattering or vapordeposition (FIG. 12H and S38 of FIG. 13).

(9) Finally, the protective layer 47 is coated on the entire reflectingfilm 46 to complete the optical disk 31 (FIG. 121 and S39 of FIG. 13).

Recording and reproduction on this optical disk 31 will now bedescribed.

FIG. 14 illustrates an optical disk drive device 50 applicalbe to thisoptical disk 31.

The optical disk 31 is driven and rotated by a spindle motor 51 at aconstant linear velocity. An optical pickup 52 as laser beam irradiationmeans and laser beam detect ion means is provided at a position oppositeto the recording surface of the optical disk 31. The optical pickup 52is driven by a feed motor 53 in the radial direction of the optical disk31.

In the reproduction mode, a read out signal from the optical disk 31 isamplified by an RF (high-frequency) amplifier 54 and is supplied to anEFM-CIRC (cross interleaved Read-Solomon code) encoder-decoder 55. Theencoder-decoder 55 subjects the amplified signal to EFM demodulation andCIRC decoding and supplies its output data to a buffer memory 57 to beonce stored therein under the control of a memory controller 56 andsupplies control information to a system controller 58. Data which isonce stored in the buffer memory 57 is sequentially read out under thecontrol of the memory controller 56 and supplied to an unillustratedhost system. A servo control sect ion 59 performs focusing and trackingcontrols of the optical pickup 52 in response to the output of the RFamplifier 54 and also controls the spindle motor 51 and the feed motor53 in accordance with a command from the system controller 58.

In the recording mode, data to be recorded stored in the buffer memory57 is read out through the memory controller 56 and is subjected to CIRCand EFM by the EFM-CIRC encoder-decoder 55 to be converted to a recordsignal. The record signal is supplied to the optical pickup 52 throughthe RF amplifier 54. The optical pickup 52 modulates laser beam with therecord signal and forms record pits on the optical disk 31. In the RAMarea 33 and the WO area 34 of the optical disk 31, wobble is formed inthe grooves 43. An address decoder 60 generates record address of theoptical disk 31 in response to a signal provided by reading this wobbleby the optical pickup 52 and this address information is supplied to theencoder-decoder 55.

Examples of recording and reproduction of the optical disk 31 by usingthe above described optical disk drive device 50 are shown in FIGS. 15Aand 15B.

FIG. 15A shows an example of recording final processed data in the WOarea 34.

In a floppy disk or other various types of recording media, overwriteinhibit can be made. Such overwrite inhibit however is applied to themedia as a whole and the media cannot cope with a demand for overwritinga part of data. For performing overwriting, the overwrite inhibit of themedia must be removed. In this case, there occurs a case where the usererroneously overwrites data on other necessary data. In the presentexample, therefore, occurrence of such error is prevented by using theRAM area 33 as a draft area and the WO area 34 as a fair copy area.

More specifically, data file etc. which the user uses are recorded inthe ROM area 32. Necessary data is read from the ROM area 32 (541).Then, this data is processed or new data is added to this data (S42) andresulting data is overwritten In the RAM area 33 (S43). Since rewritingcan be made any number of times in the RAM area 33, the user can amendthe data until he is finally satisfied. Upon completion of processing ofdata (S44), finally processed data is recorded in the WO area 34 (S45).Data which is recorded in the WO area 34 is in the same state asoverwrite inhibit has been applied to it. Thus, overwrite inhibit can beapplied only to important data so that convenience in the use of theoptical disk 31 is improved.

FIG. 15B shows an example of recording best data in a game in the WOarea 34.

In a role playing game, for example, there arises a case where a gameuser desires to preserve information of a cleared stage and informatonrequired for clearing. In a shooting game, points gained in each stageis important information and, hence, the game user may desire topreserve this information in addition to information of a cleared stage.Thus, the game user desires to preserve information of the highest pointgained and the most advanced stage cleared as the best results clearedwhile he desires to play the game and renew points and advance to afurther stage. Since points gained cannot be renewed each time, he maysometimes desire to proceed further from a state where he has gained thebest data. Further, games tend to become large-scaled including manyintermediate information such as points gained and techniques.

In the present example, the best data is recorder in the WO area 34 andcurrently proceeding data is recorded in the RAM area 33. First, at thestart of the game, the ROM area 32, the RAM area 33 and the WO area 34are read out (S51) and selection is made as to whether the game isstarted newly, or the game is started by using data of the RAM area 33or the game is started by using data of the WO area 34 (S52). As aresult of the selection, data is read out and the game is started ($53).Data during progress of the game is successively recorded in the RAMarea 33 (S54). When the best data is gained (S55), the data is shiftedto the WO area 34 (S56) If the WO area 34 is selected in the step 52,the game is started from the best score state.

As described above, according to this embodiment, convenience in the useof the optical disk 31 can be improved. In this embodiment, the ROM areais not essential but an optical disk having the RAM area and the WO areaonly can achieve the advantageous result of the invention.

What is claimed is:
 1. An optical disk comprising: a first area of apredetermined recording density formed on an inner peripheral side ofthe optical disk; a second area of a higher recording density than thepredetermined recording density formed on an outer peripheral side ofthe optical disk; and a program recording area provided in each of thefirst and second areas in which an independent program is respectivelyrecorded, wherein a depth from a surface on which a laser beam isirradiated to a recording surface of the second area is smaller than adepth from the surface on which the laser beam is irradiated to arecording surface of the first area.
 2. An optical disk comprising: afirst area of a predetermined recording density formed on an innerperipheral side of the optical disk; and a second area of a higherrecording density than the predetermined recording density formed on anouter peripheral side of the optical disk, wherein the first area has, alead-in area and a first program area and the second area has a secondprogram area and a lead-out area, TOC information of the first programarea and the second program area being recorded in the lead-in area ofthe first area, and the optical disk has a single lead-in area and asingle lead-out area.
 3. An optical disk comprising: a rewritable areaon which recorded information is rewritable; and a write once area,provided on an outer peripheral side of the rewritable area, which issusceptible to being recorded on only once, said write once area beinginitially in an unrecorded state.
 4. An optical disk comprising: arewritable area on which recorded information is rewritable; a writeonce area, provided on an outer peripheral side of the rewritable area,which is susceptible to being recorded on only once; and a read-onlyarea which is susceptible to be read from, but not written to.
 5. Amethod of recording information in an optical disk, comprising arewritable area which is adapted to be recorded onto more than once anda write once area which is adapted to be recorded onto once comprisingthe steps of: recording data on the rewritable area; overwriting thedata recorded on the rewritable area when the data is renewed;recording, in accordance with a predetermined command, the data whichhas been recorded in the rewritable area in the overwriting step in thewrite once area as overwrite inhibit information.
 6. An optical diskcomprising: an area of a predetermined recording density; and an area ofa higher recording density than the predetermined recording density,wherein a depth from a surface on which a laser beam is irradiated to arecording surface of the area of the higher recording density is smallerthan a depth from the surface on which the laser beam is irradiated to arecording surface of the area of the predetermined recording density. 7.An optical disk comprising: a first area of a recording density of afirst linear velocity; a second area of a recording density of a secondlinear velocity which is lower than the first linear velocity; and aborder area between the first area and the second area where recordingdensity changes gradually from the recording density of the first areato the recording density of the second area.
 8. An optical diskcomprising: a first area of a predetermined recording density; and asecond area of a higher recording density than the predeterminedrecording density, wherein the first area has a lead-in area and a firstprogram area, and the second area has a second program area and alead-out area, TOC information of the first program area and the secondprogram area is recorded in the lead-in area of the first area, and theoptical disk has a single lead-in area and a single lead-out area.
 9. Anoptical disk comprising: a first area of a predetermined recordingdensity formed on an inner peripheral side of the optical disk; and asecond area of a higher recording density than the predeterminedrecording density formed on an outer peripheral side of the opticaldisk, wherein the first area has a lead-in area and a program area andthe second area has a program area and a lead-out area, TOC informationof the program areas of the first and second areas being recorded in thelead-in area of the first area, further including a border area betweenthe first area and the second area, wherein the border area is adaptedso that when an optical pickup, detecting a laser beam which has beenirradiated on a recording surface of the optical disk and reflectedtherefrom, moves to an object point across the border area, a feeddistance of the optical pickup from an end point of the border area tothe object point is calculated before the optical pickup reaches astarting point of the border area.
 10. An optical disk as defined inclaim 3 wherein the optical disk is rotated at a constant linearvelocity.
 11. A method of recording information in an optical disk asdefined in claim 5 wherein the rewritable area is provided on an innerperipheral side of the write once area.
 12. A method of recordinginformation in an optical disk as defined in claim 5 wherein the data isa game score obtained by carrying out a game.
 13. An optical disk asdefined in claim 7 wherein the second area is provided on an outerperipheral side of the first area.
 14. An optical disk as defined inclaim 8, further including: a border area which is a mirror areaprovided between said first area and said second area.